The production and recovery of petroleum sulfonates is well-known in the art. Typically, a hydrocarbon feed stock such as natural or refined petroleum oil is treated with a sulfonating agent such as fuming sulfuric acid, sulfur trioxide or oleum (sulfur trioxide dissolved in sulfuric acid). This treatment produces oil soluble sulfonic acids, commonly known as "mahogany acids" and water soluble sulfonic acids, commonly known as "green acids" as well as a number of other by-products including unused acid, sulfates, sulfites, and acid sludge. Additional byproducts include unreacted hydrocarbon oil which is commonly known as "white oil."
In the majority of the prior art sulfonation processes, the desired oil soluble sulfonates are recovered by washing the treated hydrocarbon feed stock with ammonia or caustic soda (sodium hydroxide) to neutralize the oil soluble sulfonic acids and then extracting the sodium sulfonates so produced with a solvent such as water, alcohol, low molecular weight hydrocarbons, or mixtures of these compounds.
The extracted sodium sulfonate can then be converted into polyvalent metal sulfonates such as calcium, barium, or other metal sulfonate by treatment of the sodium sulfonate with the appropriate salt. Such conversion usually takes place after purification to remove residual inorganic salt and green acid sulfonates. For example, treatment of the sodium sulfonate with excess calcium chloride will produce calcium sulfonate and sodium chloride. The sodium chloride can then be removed with the excess calcium chloride though residual chloride ion will remain with the metal sulfonate.
Attempts to avoid this two-step neutralization and conversion process by the direct neutralization of sulfonic acid with calcium chloride have been unsuccessful because of the formation of troublesome calcium sulfate slime and because of the difficulty of separating undesirable water soluble green acid sulfonates from oil soluble sulfonates when both are in the form of their calcium soaps.
One method of reducing the amount of green sulfonic acid is to reduce the relative proportion of paraffinic or long-chain hydrocarbon molecules in the petroleum feed stock because the oil soluble sulfonic acids are produced from the sulfonation of the aromatic portion of hydrocarbon feed stocks. Other methods rely on the previously described neutralization and two-phase hydrocarbon solvent and water extraction technique followed by conversion to the desired polyvalent metal sulfonate form. While the polyvalent metal salts of mahogany sulfonic acid are oil soluble and almost entirely insoluble in water, the readily water soluble polyvalent metal salts of green sulfonic acid are partially oil soluble when in the presence of oil soluble acid salts. Because the oil soluble polyvalent metal sulfonates are often used as detergent and rust preventative additives to lubricating oils, the presence of water soluble green sulfonic acid is objectionable in lubricating applications where moisture may be encountered. Even a relatively small proportion of water soluble sulfonate may result in excessive water corrosion of lubricated metal components.
Accordingly, because of the complexity and attendant expense associated with these prior art methods for the production and recovery of oil soluble polyvalent metal sulfonates, it is a principal object of the present invention to provide a method for the direct production and recovery of oil soluble polyvalent metal sulfonates without the use of a preliminary sodium hydroxide or ammonia neutralization step.
It is an additional object of the present invention to provide a method for the direct production of oil soluble polyvalent metal sulfonates which are free from water soluble sulfonates or that contain water soluble sulfonates in insignificant proportions so that the polyvalent metal sulfonates are suitable for use in compound lubricants.
It is a further object of the present invention to disclose a method for the production of oil soluble polyvalent metal sulfonates having only negligible levels of chloride ions, sulfate ions and sulfite ions.
It is a further object of the present invention to provide a method for the production and recovery of oil soluble polyvalent metal sulfonates in which the sulfonates can be readily recovered through filtration without the need for diatomaceous earth.